1. Field of the Invention
The present invention relates to the production of rayon fibres, filaments or films with a viscose process. More particularly, it relates to an improved process for spinning a viscose solution into an acidic spinbath containing no zinc salt.
2. Description of the Related Art
The production of regenerated cellulosic products like rayon fibre, films and filaments by viscose process, involves an initial step the conversion of a cellulosic material to alkali cellulose by treatment with caustic soda solution. The alkali cellulose is then shredded, aged and further converted into cellulose xanthate by treatment with carbon disulphide. The xanthated cellulose is then dissolved in dilute sodium hydroxide solution to obtain desired content of cellulose and alkali. The solution so obtained is called viscose which is further filtered, ripened, deaerated and then extruded through a spinnerette into a spin bath mainly comprising of sulphuric acid, zinc sulphate and sodium sulphate.
The spinbath of conventional process essentially contains zinc sulphate or some other soluble zinc salts which acts as a regeneration retardant. Zinc salts present in either viscose or in spinbath forms zinc xanthate salts in the filament, which is a more stable compound than sodium cellulose xanthate and thereby allows the stretching phenomenon of filaments. Zinc is known to be highly toxic chemical and the presence of even in ppm range in effluent is objectionable specially for drinking purposes and marine lives. Other than pollution problem, the high use of zinc sulphate in viscose process has certain other notable disadvantages. It is expensive and it has also, to a certain degree, the tendency to form encrusting deposits on spinning equipments.
In addition to zinc sulphate in spin bath, the other viscose modifiers are also used like polyethylene glycols, polyethylene oxides, certain amines, formaldehyde, etc. as auxiliary regeneration retardants, specially when high strength fibres are required. All these viscose organic modifiers not only cause processing difficulties but also pose a serious problem of air and stream pollution. They are also associated with adverse physiological effects.
It was, therefore, thought desirable at least in certain commercial applications like production of regular rayon to develop a process which is completely zinc free.